The present invention relates to a flexible tubular pipe for transporting hydrocarbons, of the type comprising, placed radially from the inside outward, a carcass, an internal pressure sheath and one or more armor plies, the carcass being formed by the winding, with interlocked turns, of a profiled elongate element of metal strip type.
Such a pipe is commonly called a “rough bore” pipe because the carcass which constitutes the inner layer of the pipe has obvious discontinuities at the gaps separating the turns, unlike what are called “smooth bore” pipes in which the innermost layer of the pipe is formed by an inner sheath covering the inside of the vault.
Such a pipe may optionally include, in addition to the layers mentioned, other special layers, such as a pressure vault, a hoop layer, intermediate sheaths, an external protection sheath, etc.
The carcass is, as the API 17J recommendations by the American Petroleum Institute recall, a tubular layer, in principle an inner layer, formed from an interlocked metal winding intended essentially to prevent the collapse of the internal sealing sheath or of the pipe in the absence of internal pressure in the pipe, owing to the effect of the external pressure, of the pressure generated by the tensile armor plies or even of the external mechanical loads (especially in the gripping members used for laying the pipe).
The carcass is most conventionally made of corrosion-resistant metal strip, generally shaped with a cross-section similar to a couched “S” and wound in such a way as to produce turns that interlock with one another. In order to improve the performance of a carcass, various proposals have already been made. Reference may thus be made to document EP 0 429 357 by the Applicant, which discloses a carcass in which the constituent metal strip comprises a wave forming a bearing structure that increases the height of the cross-section and therefore the inertia, thus improving the crush resistance of the carcass.
Although this solution seems simple to implement, in practice it appears that the operation of precisely forming the wave is difficult. Wave formation on the border of the metal strip requires large forces on the profiler—it turns out that the strip slips under these forces, which results in the geometry of the profiled element being unbalanced, causing problems both in the pitch and the inertia of the interlocked profiled element. These problems may reduce the crush resistance of the carcass.
The Applicant has also proposed in document WO 03/036152, for certain applications, a carcass formed by the winding of at least one elongate metal element of large cross-section which is corrosion-resistant and interlocked by a thin corrosion-resistant metal strip.